Liquid containers which are used as reagent liquid vessels in automatic analyzers can have reagent liquid extracted from them by automatic pipetting. In general, the pipetting takes place, in more modern systems, at high speeds in order to allow a high throughput of relevant analysis operations. The liquid containers are typically supplied quickly to the pipetting station by a method of transporting, e.g. by a rotor, and are stopped in a pipetting zone of the pipetting station, whereupon an automatic pipette or suction needle penetrates the top opening of the liquid container through an extraction chimney in order to extract liquid in the liquid container by suction.
For the example of automatic high throughput analyzers, an extremely short cycle time of only a few seconds is allowed for each individual pipetting operation, which includes the positioning of the liquid container in the pipetting zone. This short cycle time gives rise to the problem where, when the liquid container is stopped abruptly in the pipetting zone, the liquid sloshes in the container and possibly sprays upwards. A typical waiting period for the liquid to settle in the container is typically longer than the short pipetting cycle time required for high throughput operation. Pipetting in the presence of a fluctuating liquid level in the extraction chimney typically should be avoided since a relatively large region of the outside of pipette tip may become undesirably wetted with the liquid and a comparatively large volume of liquid may remain on the outside of the pipette tip as the pipette is withdrawn from the liquid container. This remaining liquid then may give rise to contamination in further pipetting operations.
In order to avoid this possible source of contamination, the pipette tip, during pipetting, should only penetrate the slightest possible amount of liquid in the container. Therefore, the liquid in the liquid container should be, as much as possible, at rest. Additionally, the pipette should also avoid encountering air on account of a fluctuating liquid level. Further still, the formation of foam in the extraction chimney should be prevented.
Regarding prior art relating to reaction liquid containers with an extraction chimney, reference may be made, for example, to WO 97/12677 A1, to U.S. Pat. No. 5,102,631 or to DE 38 38 278 C1. In the case of the liquid container disclosed in WO 97/12677 A1, a tubular extraction chimney is provided with a radially outwardly projecting flange at its top end. The tubular extraction chimney is supported by the projecting flange in a hanging state on a nozzle of the liquid container top opening. The completely open bottom end of the extraction chimney extends to the vicinity of the base of the liquid container. Liquid communication between the extraction chimney and the interior region of the liquid container which encloses the extraction chimney can take place only via a narrow base gap at the bottom opening of the extraction chimney. In order for pressure equalization to take place between the interior of the liquid container and the surroundings during pipetting, slot-like wall-thickness reductions are provided in the top region of the extraction chimney. These reductions are intended to allow air to flow in between the opening nozzle at the top of the liquid container and the lateral surface of the extraction chimney.
DE 38 38 278 C1 discloses a liquid container having an extraction chimney with a cross section that is significantly smaller than the cross section of the top opening of the liquid container. The extraction chimney passes through the top opening and is affixed to a screw top. The screw top is screwed to an opening nozzle. A through-hole in the screw top allows pressure equalization between the liquid container interior and the external surroundings. The extraction chimney extends into the liquid container to the vicinity of the container base. The exchange of liquid between the extraction chimney and the liquid container interior takes place by way of the open underside of the extraction chimney. In a further exemplary embodiment disclosed in DE 38 38 278 C1, the outer circumference of top end of the extraction chimney and the inner circumference of the nozzle which encloses the top end of the extraction chimney are only slightly different. In this case, there is no ventilation path of sufficient magnitude for pressure equalization between the liquid container interior and the surroundings between the outside of the extraction chimney and the inner surface of the opening nozzle. For pressure-equalization purposes, a through-bore is provided in the lateral surface of the top end of the extraction chimney. The extraction chimney is essentially completely open at its bottom end. Spacing webs are provided at the bottom end of the extraction chimney.
The liquid container disclosed in U.S. Pat. No. 5,102,631 is of similar construction to the second exemplary embodiment from DE 38 38 278 C1 and thus likewise has a through-hole in the lateral surface of top end of the extraction chimney. The extraction chimney extends through the liquid container to the vicinity of the base of the liquid container. Large lateral openings are provided in the lateral surface at the bottom end of the extraction chimney.
In accordance with the basic functional principle of the extraction chimney, a small spacing is typically formed between the bottom of the extraction chimney and the container base located opposite the extraction chimney bottom. Therefore, a narrow flow gap for forming high flow resistance exists. Fluctuations in the liquid container volume outside the extraction chimney can act within the extraction chimney at best in a damped state. The known extraction chimneys thus typically have, in their bottom regions adjacent to the container base, a liquid-permeable zone with a low level of liquid permeability.
However, this restriction of the liquid permeability, which is necessary for the desired functioning of the extraction chimney, is also associated with a disadvantage. Namely, such liquid containers initially have to be filled with liquid through the top opening of the extraction chimney. Filling has to take place very slowly because of the low level of liquid permeability in the liquid-permeable zone. The filling liquid level in the extraction chimney rises much more quickly than the filling liquid level in the liquid container outside the extraction chimney. Therefore, filling the liquid container too quickly may result in the liquid overflowing at the top opening of the liquid container.
Even conventional liquid containers in which the extraction chimneys are to be inserted after the liquid has been introduced into the liquid containers may have the problem of overflow of liquid through the top container openings. Overflow can only be avoided if the extraction chimneys are introduced comparatively slowly into the liquid containers due to the low level of liquid permeability in the liquid-permeable zones in order to prevent the liquid from rising up too quickly into the bottom end of the extraction chimneys.
It is against the above background that the present invention provides a liquid container that can be filled, if required, quickly through the top opening and through the extraction chimney and that, during liquid-extraction operation, has a settled liquid level within the extraction chimney in comparison to any fluctuations in the liquid container region outside the extraction chimney.